Jade gets her first tattoo shortly visiting her brother when she is fifteen.
It's a star on her right forearm that got her grounded for six weeks (in theory). Like everything Jade does, the tattoo has meaning.
Mostly, it's about Beck. He is the one shining spot in Jade's life. Her star. It's her way of saying that she belonged with (but never to) him.
She chooses red because red is his favorite color. She prefers black, but sees the appeal of red. It's the color of blood, of passion; of courage and fire.
(And, though she would never admit it, if Cat were to lay her head on Jade's arm, it would match.)